In many filtration systems, filter units are disposed inside a filter housing that defines the flow path into and out of the filter units. In some applications, the filter housing can be very deep. Although it is possible to manufacture a single filter unit having a length corresponding to the depth of the filter housing, such a filter unit would require different manufacturing processes or equipment for each specific length of filter unit manufactured. Therefore, filtration systems commonly employ a modular concept in which a plurality of short filter units are manufactured and then connected end to end at the time of installation to form a stack of filter units having the necessary length. The stack is referred to by the number of filter units it contains. For example, a stack of two, three, or four filter units connected together in this manner is called a twohigh, a three-high, or a four-high stack. Some filter housings may require only a single filter unit, which may then be referred to as a one-high stack. The modular concept is popular among filter manufacturers because it reduces the number of different lengths of filter units that need to be manufactured and kept in inventory.
When a plurality of filter units are connected together in a stack, it is necessary to form a fluid-tight seal between adjacent filter units. Various arrangements have been proposed in the past for connecting the filter units of a stack so as to obtain a fluid tight seal. In some arrangements, adjoining filter units are welded together. In other arrangements, adjoining filter units in a stack are mechanically connected by separate coupling members, each being individually connected to the end cap of each filter unit. Such connections rely on the strength of the coupling members to form a fluid-tight seal between the filter units, which results in the coupling members and the end caps of the filter units being undesirably heavy. Furthermore, since a fluid-tight fit is attained between the filter units by the coupling members, the dimensions of the coupling members and the end caps must be extremely accurate. Consequently, they are expensive to manufacture. The need for separate coupling members and end caps also increases manufacturing and installation costs. In addition, the coupling members may protrude into the path of fluid flow through the filters and increase the resistance to flow.